一．数码管简要介绍
数码管分为共阳极数码管和共阴极数码管。共阳数码管是指将所有发光二极管的阳极接到一起形成公共阳极(COM)的数码管，共阳极（COM）需接+5V才能使其工作。共阴数码管是指将所有发光二极管的阴极接到一起形成公共阴极(COM)的数码，共阴极（COM）需接GND才能使其工作。如下图:
下面是数码管的编码：
（1）共阳极数码管：
位选为高电平（即1）选中数码管；
各段选为低电平（即0接地时）选中各数码段；
由0到f编码为:
parameterSEG_NUM0=8'hc0,
SEG_NUM1=8'hf9,
SEG_NUM2=8'ha4,
SEG_NUM3=8'hb0,
SEG_NUM4=8'h99,
SEG_NUM5=8'h92,
SEG_NUM6=8'h82,
SEG_NUM7=8'hF8,
SEG_NUM8=8'h80,
SEG_NUM9=8'h90,
SEG_NUMA=8'h88,
SEG_NUMB=8'h83,
SEG_NUMC=8'hc6,
SEG_NUMD=8'ha1,
SEG_NUME=8'h86,
SEG_NUMF=8'h8e;
（2）共阴极数码管：
位选为低电平（即0）选中数码管；
各段选为高电平（即1接+5V时）选中各数码段；
由0到f的编码为:
parameterSEG_NUM0=8'h3f,
SEG_NUM1=8'h06,
SEG_NUM2=8'h5b,
SEG_NUM3=8'h4f,
SEG_NUM4=8'h66,
SEG_NUM5=8'h6d,
SEG_NUM6=8'h7d,
SEG_NUM7=8'h07,
SEG_NUM8=8'h7f,
SEG_NUM9=8'h6f,
SEG_NUMA=8'h77,
SEG_NUMB=8'h7c,
SEG_NUMC=8'h39,
SEG_NUMD=8'h5e,
SEG_NUME=8'h79,
SEG_NUMF=8'h71;
二．74HC595简要介绍
74HC595是8位串行输入/8位串行或并行输出的存储状态寄存器，内部具有有8位移位寄存器和一个存储器，具有三态输出功能，可由SPI接口直接驱动。其引脚图如下：
74HC595控制线主要有SHCP：移位寄存器时钟（上升沿有效）；STCP：存储器时钟（上升沿有效）；DS：串行移位输入；Q7’：串行输出；Q0-Q7：并行输出；OE：使能端（低电平有效）；MR：异步复位端（低电平有效）。
内部逻辑示意图：
74HC595控制时序图：
三．74HC595驱动数码管电路图
四．FPGA控制74HC595驱动数码管思路
由FPGA控制74HC595驱动数码管其实主要是抓住74HC595的控制时序，进而输出所需控制显示的内容，由同步状态机实现。
1.首先，要想74HC595工作起来，得有时钟输入。由于74HC595的数据输入是串行输入，所以我们需要产生第一个时钟---串行移位时钟：shcp。根据芯片手册上所写的在VCC=3.0V时的最大时钟频率为15M，因而，在这里我选取shcp=10M，用简单的计数器对50M全局时钟进行5分频得到。
2.下面到了关键时候了，已经产生shcp串行移位时钟驱动74HC595移位寄存器工作了，但什么时候由FPGA传送数据呢？由于74HC595是在shcp时钟上升沿读取数据，所以为了确保FPGA传送的数据被准确地接收下来，在FPGA里面，我选取shcp时钟的下降沿发送数据。这里可以理解成SPI协议传输，FPGA为主机，74HC595为从机，主机在下降沿发送数据，从机在上升沿读取数据。在代码里，我采用边沿检测技术来捕获shcp时钟的下降沿，这个技术读者需要好好体会把握，很有用处。
3.到了这步，数据已经能正常移位进入74HC595串行移位寄存器了。这里我们要开始思考数码管的问题了，根据上面电路图可以知道，要完全将8位数码管的段选数据和位选数据传给数码管，需要24个状态，即：完成一次数码管的显示驱动需要产生24个shcp时钟。在移位数据完全进入移位寄存器时，产生一个stcp存储器时钟上升沿，把有效数据传入数码管。具体实现方式请参考代码理解。
4.一次数码管的显示驱动已经在前面几步完成了，如果要进行动态显示的话，就需要数码管循环扫描了，每一次扫描，执行位选数据变换，段选数据变换即可。
五．Verilog代码
本代码主要实现了8位数码管集体同步从0-F循环计数，动态显示。
+ 查看代码
/***************************************************************
**************name: seg_595************
*********author: zzuxzt*********
**************time: 2014.5.21***************
***************************************************************/
module seg_595(input clk,
input rst_n,
output shcp, //shift clk
output stcp, //latch clk
output seg_data);
/********************Common code****************/
//------------duan xuan------------------------
parameter SEG_NUM0 = 8'h3f,//c0,
SEG_NUM1 = 8'h06,//f9,
SEG_NUM2 = 8'h5b,//a4,
SEG_NUM3 = 8'h4f,//b0,
SEG_NUM4 = 8'h66,//99,
SEG_NUM5 = 8'h6d,//92,
SEG_NUM6 = 8'h7d,//82,
SEG_NUM7 = 8'h07,//F8,
SEG_NUM8 = 8'h7f,//80,
SEG_NUM9 = 8'h6f,//90,
SEG_NUMA = 8'h77,//88,
SEG_NUMB = 8'h7c,//83,
SEG_NUMC = 8'h39,//c6,
SEG_NUMD = 8'h5e,//a1,
SEG_NUME = 8'h79,//86,
SEG_NUMF = 8'h71;//8e;
//--------------wei xuan----------------------
parameter wei_all = 8'b0000_0000;
/****************************seg display data**********************************/
//---------------------data conventer----------------------------
reg [7:0] seg_num;
wire [7:0] wei_data;
assign wei_data = wei_all;
always@(posedge clk or negedge rst_n)
begin
if(!rst_n)
begin
seg_num <= 1'b0;
end
else
begin
case(data)
8'h0: seg_num <= SEG_NUM0;
8'h1: seg_num <= SEG_NUM1;
8'h2: seg_num <= SEG_NUM2;
8'h3: seg_num <= SEG_NUM3;
8'h4: seg_num <= SEG_NUM4;
8'h5: seg_num <= SEG_NUM5;
8'h6: seg_num <= SEG_NUM6;
8'h7: seg_num <= SEG_NUM7;
8'h8: seg_num <= SEG_NUM8;
8'h9: seg_num <= SEG_NUM9;
8'ha: seg_num <= SEG_NUMA;
8'hb: seg_num <= SEG_NUMB;
8'hc: seg_num <= SEG_NUMC;
8'hd: seg_num <= SEG_NUMD;
8'he: seg_num <= SEG_NUME;
8'hf: seg_num <= SEG_NUMF;
default: seg_num <= SEG_NUM0;
endcase
end
end
//------------------1s counter-----------------------
reg [31:0] cnt;
reg [7:0] data;
always@(posedge clk or negedge rst_n)
begin
if(!rst_n)
begin
cnt <= 1'b0;
data <= 1'b0;
end
else if(cnt==32'd50000000)
begin
cnt <= 1'b0;
if(data==8'hf)
data <= 1'b0;
else
data <= data + 1'b1;
end
else
cnt <= cnt + 1'b1;
end
/*****************************seg driver*************************************/
//---------------shift clk----------------------
reg [2:0] cnt_st;
reg shcp_r;
always@(posedge clk or negedge rst_n)
begin
if(!rst_n)
begin
cnt_st <= 1'b0;
shcp_r <= 1'b1;
end
else if(cnt_st==3'd4)
begin
cnt_st <= 3'd0;
shcp_r <= ~shcp_r; //10M
end
else
cnt_st <= cnt_st + 1'b1;
end
//--------------------capture the shift clk trailing edge----------------------
reg shcp_r0,shcp_r1;
wire shcp_flag;
always@(posedge clk or negedge rst_n)
begin
if(!rst_n)
begin
shcp_r0 <= 1'b1;
shcp_r1 <= 1'b1;
end
else
begin
shcp_r0 <= shcp_r;
shcp_r1 <= shcp_r0;
end
end
assign shcp_flag = (~shcp_r0 && shcp_r1) ? 1'b1:1'b0; //shcp_clk negedge
//-----------------------------seg display state----------------------------
reg [4:0] state;
reg stcp_r;
reg seg_data_r;
always@(posedge clk or negedge rst_n)
begin
if(!rst_n)
begin
state <= 1'b0;
stcp_r <= 1'b1;
seg_data_r <= 1'b0;
end
else if(shcp_flag)
begin
case(state)
//--------------------duan xuan--------------------------
5'd0: begin
seg_data_r <= seg_num[7];
stcp_r <= 1'b1;
state <= state + 1'b1;
end
5'd1: begin
seg_data_r <= seg_num[6];
state <= state + 1'b1;
end
5'd2: begin
seg_data_r <= seg_num[5];
state <= state + 1'b1;
end
5'd3: begin
seg_data_r <= seg_num[4];
state <= state + 1'b1;
end
5'd4: begin
seg_data_r <= seg_num[3];
state <= state + 1'b1;
end
5'd5: begin
seg_data_r <= seg_num[2];
state <= state + 1'b1;
end
5'd6: begin
seg_data_r <= seg_num[1];
state <= state + 1'b1;
end
5'd7: begin
seg_data_r <= seg_num[0];
state <= state + 1'b1;
end
5'd8: begin
seg_data_r <= seg_num[7];
stcp_r <= 1'b1;
state <= state + 1'b1;
end
5'd9: begin
seg_data_r <= seg_num[6];
state <= state + 1'b1;
end
5'd10: begin
seg_data_r <= seg_num[5];
state <= state + 1'b1;
end
5'd11: begin
seg_data_r <= seg_num[4];
state <= state + 1'b1;
end
5'd12: begin
seg_data_r <= seg_num[3];
state <= state + 1'b1;
end
5'd13: begin
seg_data_r <= seg_num[2];
state <= state + 1'b1;
end
5'd14: begin
seg_data_r <= seg_num[1];
state <= state + 1'b1;
end
5'd15: begin
seg_data_r <= seg_num[0];
state <= state + 1'b1;
end
//-----------------------wei xuan------------------------------
5'd16: begin
seg_data_r <= wei_data[0];
state <= state + 1'b1;
end
5'd17: begin
seg_data_r <= wei_data[1];
state <= state + 1'b1;
end
5'd18: begin
seg_data_r <= wei_data[2];
state <= state + 1'b1;
end
5'd19: begin
seg_data_r <= wei_data[3];
state <= state + 1'b1;
end
5'd20: begin
seg_data_r <= wei_data[4];
state <= state + 1'b1;
end
5'd21: begin
seg_data_r <= wei_data[5];
state <= state + 1'b1;
end
5'd22: begin
seg_data_r <= wei_data[6];
state <= state + 1'b1;
end
5'd23: begin
seg_data_r <= wei_data[7];
stcp_r <= 1'b0; //latch the all data
state <= 1'b0;
end
default: state <= 5'bxxxxx;
endcase
end
end
assign shcp = shcp_r1; //output to drive 74HC595 shift reg
assign stcp = stcp_r; //output to drive 74HC595 latch reg
assign seg_data = seg_data_r;
endmodule
六．Modelsim仿真图
畅学电子
